The present invention relates generally to an improved grate arrangement for use in gasification systems, and more particularly to such a grate arrangement in a fixed-bed coal gasifier with the grate arrangement incorporating clinker crushing capabilities together with selective gas and solids flow distribution.
The gasification of coal and other carbonaceous materials such as peat and biomass provides for the production of product gases having high energy values useful in various energy consuming applications such as gas-fired turbine systems. The gasifiers used for the conversion of coal to such product gases include moving bed gasifiers or fixed-bed gasifiers which normally comprise a vertical reaction vessel containing a gasification zone overlying a grate mechanism which supports the downwardly moving solid reactants in the gasification zone. In addition to supporting the solid reactants, the grate mechanism, which may be of a planar or conical configuration provides for the removal of spent solid reactants or ash from the gasification zone as well as other functions including the distribution of gaseous reactants, normally air and steam, that are introduced into the base region of the gasifier and pass upwardly into the gasification zone through the grate mechanism to react with and gasify coal introduced into the top region of the gasifier.
Clinkers formed of fused ash particulates are commonly produced in the lower region of the gasification zone during the gasification process with the extent of such clinker formation being dependent upon the characteristics of the coal and the operational parameters employed in the gasification process. While proper control of steam and air flow is commonly used to limit the extent of clinker formation, crushing of the clinkers which are formed into solids of a size which will pass through or around the edges of the grate mechanism is often required in order to prevent taking the gasifier off-line for removing "excessive" clinkers. Such crushing of clinkers has been achieved by providing the grate mechanism with clinker crushing capabilities such as by employing one or more excentric lobes on the rotating grate and a "wear" ring on the stationary internal diameter.
In order to provide for the distribution of the upwardly flowing reactant gases within the gasification zone, the grate mechanisms are usually provided with throughgoing orifices or passageways placed at various locations about the surface of the grate mechanism. It was previously generally accepted that the grate mechanism should distribute these reactant gases and cause the downflow of solids through the gasification to occur in an areally uniform manner. However, it was recently found in terms of gasifier throughput that the distribution of the upflowing gaseous reactants and the downflowing solids in the gasification zone in a non-areally uniform manner would be more advantageous from an efficiency standpoint in the gasification operation. Thus, while previously known grate mechanisms have been found to provide either a capability for satisfactorily crushing clinkers or a desirable distribution of the reactant gases, none of the previous grate mechanisms have been found to be capable of providing both effective clinker crushing and desirable reactant gas distributing characteristics nor do they address the desirability of adjusting the flow pattern of the reactant gases for effecting an areal or other distribution of the reactant gases or adjusting the flow pattern of solids in the gasification zone.